Same Here, macOS Big Sur 11.4 (20F71), MacBook Pro 13"2017. After a full shut down the colors looks normal, the images stay sharp, and the flickering stops, but after 10 to 15 minutes colors been stranger, some small flickers starts and images looks blurry and with no details. Black color turns a kind of dark green. Detail: Its occur only on native monitor, if a try side car with my iPad everything looks normal, same with tv.